Forest Ecology and Management 470–471 (2020) 118212 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco The influence of forest surroundings on the soil fungal community of black truffle(Tuber melanosporum) plantations T ⁎ Daniel Oliacha,b,c, , Carlos Colinasa,c, Carles Castañod, Christine R. Fischera, Francesc Bolañoa, José Antonio Bonetc,e, Jonàs Olivac,e a Centre de Ciència i Tecnologia Forestal de Catalunya, Crta. Sant Llorenç de Morunys km 2, 25280 Solsona, Spain b Forest Bioengineering Solutions S. A., Crta. Sant Llorenç de Morunys km 2, 25280 Solsona, Spain c Universitat de Lleida, Dept. de Producció Vegetal i Ciència Forestal, Av. Rovira Roure, 191, 25198 Lleida. Spain d Department of Forest Mycology and Plant Pathology, Uppsala BioCenter, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden e Joint Research Unit Agrotecnio-CTFC, Avda. Rovira Roure, 191, 25198 Lleida, Spain ARTICLE INFO ABSTRACT Keywords: Black truffles are a highly valued non-wood forest product. The success of truffle plantations is arousing the Afforestation interest to establish orchards within forest settings. One main concern is that the forest may act as a source of Quercus ilex ectomycorrhizal fungi that could displace Tuber melanosporum in plantations and impair truffle production. We ffl Tru e orchards studied the effects of host tree distance to the surrounding forest on T. melanosporum development and on the Fungal diversity root-associated fungal community. Our research was carried out in a 5-year old holm oak (Quercus ilex) plan- Mating types tation established in an abandoned pasture surrounded by a Q. ilex forest in the Pyrenees. The spatial distribution Niche preemtion of different fungal guilds as well as of T. melanosporum mycelium quantity and mating types frequency was correlated with the distance to the forest and the diameter of the trees. We found a higher relative abundance of non-T. melanosporum EcM fungi associated with the trees closer to the forest. Larger root collar diameter trees had greater biomass of T. melanosporum mycelium and displayed fungal community compositions less affected by the distance to the forest. No associations between the biomass of T. melanosporum mycelium in the soil and the distance to the forest or the abundance of non-T. melanosporum EcM fungi were observed. Our results in- dicate that T. melanosporum inoculated oaks planted in areas surrounded by forests may be colonised by other ectomycorrhizal species, and develop a distinct microbial community from those usually established in agri- cultural lands. Further investigations should be carried out to determine whether a different fungal community may affect truffle production in the future, but to date, truffle mycelium does not seem to be impaired. 1. Introduction which Escafré and Rousset (2006) estimated a total economic impact of − 67 million euros yr 1. Black truffle(Tuber melanosporum) plantations are being developed One of the main drivers for establishing plantations has been the across all the Mediterranean-climate regions around the world i.e. decline of wild truffle production in the last 100 years (Callot, 1999). Spain, France, Italy and Australia (Reyna and Garcia-Barreda, 2014). Both lower summer rainfall (Büntgen et al., 2015, 2019; Thomas and − The current global production is about 120,000 kg yr 1 which gen- Buntgen, 2019), and forest canopy closures seem to be the main causes erates an annual turnover of ca. 50 million euros to truffle growers (Le Tacon et al., 2014). In contrast, plantations are thriving (Sánchez (Oliach et al., 2020). Besides direct revenues, the black truffle pro- and Sánchez, 2019). Truffle orchards are produced by planting one-year duction has a positive impact in the areas where they are collected, old nursery inoculated seedlings of several oak species (Quercus spp.) favouring the development of auxiliary economic activities such as and hazelnut (Corylus avellana) at a density of ca. 250–300 trees per nursery production of mycorrhized seedlings with T. melanosporum, hectare. Truffles begin to fruit after 5–7 years of plantation, depending technical consulting, trade of truffled products, agro-tourism and re- on site conditions and management intensity. The establishment re- search (Büntgen et al., 2017). In France, where annual production of quirements for truffle orchards in agricultural land and cultural prac- truffles is about 43,000 kg yr-1 (2013–2017) (Oliach et al., 2020), for tices in terms of irrigation, weed control and fertilization have been ⁎ Corresponding author. E-mail address: [email protected] (D. Oliach). https://doi.org/10.1016/j.foreco.2020.118212 Received 2 December 2019; Received in revised form 17 March 2020; Accepted 24 April 2020 0378-1127/ © 2020 Elsevier B.V. All rights reserved. D. Oliach, et al. Forest Ecology and Management 470–471 (2020) 118212 studied (Colinas et al., 2007; Jaillard et al., 2014, 2016, Olivera et al., 2. Material and methods 2011, 2014a, 2014b; Suz et al., 2010). However, the increasing demand for truffles has raised the interest for establishing truffle plantations in 2.1. Experiment site other types of non-economically productive lands such as abandoned pastures and agricultural fields within forested settings. In May of 2010, we established a 1-ha experimental afforestation Plantations in the vicinity of forests have been historically dis- plot in a recently abandoned pasture located in the eastern Pre- couraged due to inoculum banks of competing ectomycorrhizal fungi Pyrenees of Spain (42°02′36.96′′N, 1°14′5.62′′E). The site plot is located (Frochot et al., 1990; Sourzat, 1997). Ectomycorrhizal (EcM) associa- at 996 m above sea level, has a South west aspect with minimal slope tions are mutualistic associations between higher fungi like T. mela- and it is surrounded by an extensive Q. ilex forest. The plot is located on nosporum and Gymnosperm or Angiosperm plants belonging to certain soil formation from the Jurassic period of the type Lias-malm, formed families, and the majority of EcM hosts are trees or shrubs (Brundret mainly by calcareous and calcarenite rocks. The site presents a soil with et al., 1996). Agricultural soils are assumed to be free from ectomy- a heterogeneity depth of about 40 cm with loam soil texture (USDA) corrhizal inoculum and therefore more receptive to T. melanosporum. and pH 8.03 (1:2.5 H2O). The climate is continental Mediterranean However, propagules of EcM fungi coming from surrounding forests or with 700 mm of annual precipitation. Temperatures ranges from an already present in the soil before planting can colonize the planted annual average of maximum daily temperatures of 16 °C and minimum seedlings and eventually outcompete T. melanosporum as trees grow of 4.4 °C. (Frochot et al., 1990; Reyna et al., 2006), especially during the early The plantation consisted of 249 one-year-old Q. ilex seedlings in- years of the plantation (Águeda et al., 2010; De Miguel et al., 2014). oculated with T. melanosporum purchased from a commercial nursery Theory predicts that pre-established fungal species in EcM-free areas, (Cultivos Forestales y Micológicos S.L., Torre de las Arcas, Teruel, may have a competitive advantage over other incoming EcM species Spain). Prior to planting, we confirmed T. melanosporum seedlings co- due to priority effects (Kennedy and Bruns, 2005). In nature, T. mela- lonisation according to Fischer and Colinas (1996). No other EcM fungi nosporum colonizes young oaks establishing in treeless areas (Reyna, were observed in the seedlings before planting. 2012). This observation suggests that T. melanosporum benefits from The plantation was established following standard procedures: the niche pre-emption (Bogar and Peay, 2017), in which early-arriving EcM soil was prepared by ripping to a depth of 60 cm to break up hardpans species who first occupy the root system can have a competitive ad- and promote root penetration (Oliach et al., 2005). Seedlings were − vantage over later-arriving fungi (Kennedy and Bruns, 2005; Kennedy planted in a 6 m × 6 m grid. A 2 m × 2 m polypropylene 110 g m 2 et al., 2009). This ecological strategy is the one used by growers when mulching fabric was placed surrounding each tree in order to prevent establishing nursery-inoculated T. melanosporum seedlings on agri- herbaceous competition and to maintain soil moisture during the first cultural land. We know that T. melanosporum can survive up to 4 years years after planting following Olivera et al. (2014b). The fabric was in forest soils where EcM trees have been supressed by fire or grazing double layered: black below to reduce weed germination and white (Garcia-Barreda and Reyna, 2013; Martínez de Aragón et al., 2012). above to reflect solar radiation. The fabric was specifically chosen to Nevertheless, information about the possible competition between local allow water and gas exchange in and out of the soil. EcM species and the introduced T. melanosporum in a plantation en- vironment surrounded by forest is largely missing. 2.2. Data collection Other factors, such as host growth, may play a role modulating the competition between T. melanosporum and local EcM fungi. We know Five years after planting, in March 2015, we randomly chose 28 that in plantations, larger trees harbour higher quantities of mycelium seedlings, for which we measured height, root collar diameter and the than smaller trees, and that truffle burns, i.e. zone around the host tree minimum distance to the forest. Root collar diameter was calculated as lacking herbaceous vegetation, appear earlier on fast growing trees of an average of two perpendicular calliper measurements per tree. Tree the same age (Lulli et al., 1999; Suz et al., 2008). Gaining insights on height was measured from the root collar to the top of the tree. The the interplay amongst host growth, T. melanosporum and other EcM minimum distance to the forest was obtained from a satellite image of fungi is needed.